1. Field of the Invention
The present invention relates to pie-insulated piping systems, and more specifically to a method for installing components of a leak detection system for detecting a leak in a section of piping in the case of a breakdown of the insulation in the presence of water or other contaminants or under thermal movement stresses, or the like.
2. Description of the Prior Art
There are many instances in which insulated pipelines are needed. For example, distributed HVAC (heating, ventilation and air conditioning) applications utilize chilled water for cooling and steam for heating. The chiller and boiler are typically contained in a central location and the chilled water or steam are distributed to other locations. For example, on a school campus, the chiller and boiler may be located in a power plant building. The chilled water and steam are distributed to classrooms in separate buildings.
A set of insulated pipelines is used to convey the chilled water from the chiller to other locations and back to the chiller. Another set of insulated pipelines is used to carry the steam from the boiler to the other locations and back to the boiler. The insulated pipelines are usually located underground.
Insulated pipe is conventional and commercially available. There are predominantly two types of piping systems in use: Class-A drainable dryable testable (DDT); and polyurethane or polyisocyanurate “bonded” foam systems. Both of these systems use an inner carrier pipe to convey fluid. Although steel is commonly used for the inner pipe which carries the media to be piped, copper or aluminum or other metals as well as fiberglass, PVC, and similar materials may be utilized, as well. The present application is directed toward the “bonded” foam type system. These systems utilize a steel pipe to convey fluid. Around the outside of the steel pipe is a layer of insulating foam such as, for example, polyisocyanurate foam. Around the outside of the foam is a jacket of hard thermoplastic (such as high density polyethylene, HDPE). The foam has set up or cured within the outer jacket so as to bond to the jacket and to the inner pipe. The plastic jacket protects the foam from mechanical damage and also provides a water tight seal to prevent corrosion of the steel pipe. In the bonded type system, the foam and outer jacket do not move relative to the inner pipe. In the Class-A type system, on the other hand, the insulated inner pipe is designed to move independently of the associated outer jacket. In fact, there is an air gap between the inner pie and outer carrier pipe in the class-A type system.
Various factors can affect the integrity of the bonded foam type pre-insulated piping system. For example, environmental factors which may adversely affect the integrity of the insulated system include floods, high water tables, cooling and condensation, and the like. In the case of high temperature steam lines, temperature differentials can cause the pipeline to expand and contract over time, thereby stressing the jacket and insulating material. The protective jacket of the insulated pipeline may also be punctured inadvertently by maintenance or construction operations, as where another utility line is being installed in the immediate vicinity. If the outer protective jacket is penetrated for any reason, ground water and water vapor may enter the piping system and contact the hot carrier pipe, in the case of a high temperature system, thereby creating steam. The steam will slowly boil away the foam insulation, which may result in ultimate failure of the system.
For the above reasons, various types of pipe monitoring systems have been used in the past for status detection, and in particular leak detection, in pipelines of the type under consideration. For district heating installations of the type described, leak detection and signaling has most often been accomplished by means of metallic conductors which are embedded in the thermal insulation of the pipelines. When a leak occurs, the location of the defect can then be found out by resistance measurement or also transit time measurement. The metallic conductors are usually formed of copper or Ni/Cr and usually take the form of bare wires which are incorporated into the thermal insulation which surrounds the carrier pipe, running along the length of the pipe. As previously mentioned, this insulation will generally consist of either polyurethane or polyisocyanurate foam, with the bare wires being typically incorporated into the foam during the foaming operation as apart of the pipe manufacturing operation.
During the pipeline construction phase, i.e., field installation of the pre-insulated piping, it is necessary to join successive lengths of pipe and pipe components to form the complete pipeline distribution system. The typical field installation will necessarily involve accessory or adjunct components, such as elbows, Tees, water stops, earth anchors, and the like. The electrical conductors used in the leak detection system must necessarily be connected together to provide a complete circuit, even where the insulating materials of the associated pipes are interrupted at, for example, a water stop, or other pipe component connection location.
In the case of a physical obstruction in the insulating materials of the type presented by, for example, a water stop or anchor, one method for continuing the leak detection circuit would be to provide a hole or aperture in the water stop or anchor to allow the circuit wire to pass through the obstruction. However, providing a hole in any part of the metal of the pipeline construction, such as a water stop, presents a potential leak path, making this a less than desirable solution, even if the hole is sealed in some manner at the time of the installation. It is always possible that the hole could leak over time, allowing water to pass the water stop, thereby allowing steam to eat away at the foam insulation on the other side of the water stop.
One commercially available system which is intended to address the problem of circuit continuity is sold in Europe as the ISOPLUS®, by Fjernvarmeteknik A/S of Denmark. The method for installing this system employs three separate steps. The first is the insertion of a rigid 90° fitting into the exterior of the protective jacket of the piping. Secondly, a conductive wire is connected to the fitting with a heavy duty cable. Thirdly, the wire is sealed to the fitting by heat shrinking a small tubular sleeve around the connection area.
While the above technique avoids the necessity of drilling a hole in the metal component of the pipeline which forms the obstruction, the 90° fitting interrupts the otherwise basically uniform contour of the exterior surface of the pipeline. The fitting can be bent or broken during field installation or can become entangled with other equipment. The process itself of installing the fitting and associated wiring is time consuming and labor intensive, adding significantly to the cost of the installation.
Accordingly, one object of the present invention is to provide a method for leak detection in pre-insulated piping, which avoids the problems with leak signaling conductors and circuitry of the type located in the thermal insulation surrounding the carrier pipe in the past, and which permits leakage points or regions to be reliably and accurately located.
Another object of the invention is to provide an improved method for installing the leak detection circuitry in a pre-insulated piping system of the type which requires the circuitry to be distributed over a run of pipeline by way of lines which run in the thermal insulation surrounding the carrier pipe, where the circuitry must also by-pass or traverse accessory or adjunct components of the pipeline, such as water stops, anchors, and the like.
Another object of the invention is to provide such an improved method of leak detection which is simple in design and economical to manufacture, as compared to existing systems in use in the marketplace today.